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The Planets this Month - October 2012

Mercury

October is a good time for observers located in equatorial and southern latitudes wanting to view Mercury, as it will be visible throughout the month. During this time the planet can be spotted just south of due west. When viewed half an hour after sunset from latitude of 35S (e.g. Sydney, Australia), Mercury is about 9 degrees above the horizon on October 1st. It then climbs gradually higher as the month progresses until it reaches a peak altitude of nearly 18 degrees on October 26th. On this date, Mercury also reaches greatest eastern elongation (24 degrees).

Mercury brightness changes little during October. The planet starts the month at magnitude –0.4 before fading to magnitude -0.1 at months end. Unfortunately, the planet is not suitably placed for observers from northern temperate latitudes.

Venus remains a superb morning object this month, although the magnitude of the planet fades slightly from –4.1 to –4.0. During this time, the phase of Venus increases from 71 to 81 percent. The planet starts the month in Leo before crossing into Virgo on October 23rd, remaining there for the rest of the month. During October from northern latitudes Venus rises almost 3.5 hours before the Sun. It is currently better placed for northern hemisphere observers, hence the period of visibility during October for equatorial and southern hemisphere latitudes is up to an hour or two less.

The waning crescent Moon will pass 6 degrees south of Venus on the morning of October 12.

Mars

Mars almost keeps its distance from the Sun this month as they move on their eastward journey against the fixed stars. The "Red planet" starts the month in Libra, races through Scorpius before ending the month in Ophiuchus. Now shining at magnitude 1.2, the planet is visible low down to the southwest at dusk and sets just under 2 hours after the Sun from northern temperate latitudes. The period visibility is considerable better for southern hemisphere observers.

Incidentally, Mars is now 2 AU distant from the Earth and the apparent size of the planet has now shrunk to less than 5 arc seconds; which is not much greater than that of Uranus. There are a couple of interesting phenomena during October. On October 18, a waxing crescent Moon will pass 2 degrees north of Mars and on October 20, Mars will pass less than 4 degrees north of Antares (mag. 1.0), the red supergiant star. Antares has often been called the "Rival of Mars" due to its striking deep red colour. This conjunction presents an interesting opportunity for observers to compare the colour and brightness of the two objects.

Jupiter

Jupiter is a brilliant object that now rises in the early evening for northern hemisphere observers and a little later for those located further south. It remains visible for the remainder of the night. The giant planet is located in Taurus, a few degrees to the northeast of orange/red star Aldebaran (mag. 0.9) and the large sprawling Hyades open cluster. The most famous open cluster in the sky, the Pleiades (M45), is positioned about 20 degrees to the west of Jupiter. On October 4, Jupiter reaches its stationary point and then afterwards its motion is retrograde.

As Jupiter is currently heading towards opposition in December, both the apparent magnitude and size of the planet are currently increasing. During October, Jupiter's brightness increases from magnitude –2.5 to –2.7 and the apparent size from 43 to 47 arc seconds.

Over the next few months Jupiter will dominate the evening sky. This is especially true for northern hemisphere observers; the planet appears high and bright, a sparkling jewel in the dark autumn and winter skies. It's not as good from southern latitudes as Jupiter is low down, but still unmistakable due to its brightness.

On October 5, the Moon will pass 0.9 degrees south of Jupiter. An occultation is visible from the Southern Australia and the Southern Ocean.

Saturn

Saturn passes through superior conjunction on the far side of the Sun on October 25th. The planet is located in Virgo but for northern hemisphere observers is unobservable during October. From southern and tropical latitudes, Saturn may be glimpsed low down in the dusk sky during the first part of the month before the planet is quickly lost to the Suns glare.

Uranus

Uranus (mag. 5.7) is located in Pisces just south of the "Great Square of Pegasus". The seventh planet from the Sun reached opposition at the tail end of last month and remains visible for most of the night. Uranus is located very close to star 44 Piscium, which at mag. 5.8 is almost equal in brightness. The planet for most of last month was positioned to the east of 44 Piscium before passing the star and now residing on the western side.

This is a good time to try and test how dark your skies are by attempting to spot Uranus with the naked eye. At magnitude 5.7, the planet is faintly visible to the naked eye but dark skies and good conditions are required. If your observing site is up to scratch, you should also be able to spot 44 Piscium.

Neptune

Neptune (mag. 7.8) is located in the constellation of Aquarius and visible as soon as it gets dark. To be seen, the minimum requirements for this planet are a pair of binoculars or a small telescope. The most distant planet is located four degrees south of mag. 4.2 star Ancha (theta Aquarii) and remains observable until the early hours of the morning.